1. Field of the Invention
The present invention relates to a photomask material for photomasks that are used in the photolithographic process widely used in the fields of flat panel displays such as PDPs, FEDs and LCDs, CRT shadow masks, printed circuit boards, packages, semiconductors, etc., and a process of manufacturing photomasks from the photomask material.
2. Description of Related Art
There have been known various types of photomasks, such as a Cr photomask with a chromium metal layer formed thereon, an Em photomask (emulsion photomask) with a silver halide emulsion layer formed thereon, that is used in the photolithographic process in the fields of flat panel displays, CRT shadow masks, printed circuits boards, semiconductors, etc. Such the photomasks are disclosed in “Photo Application,” (published June, 1992 by Japan Photo Application Association, Education Branch), pages from 67 to 80. In the process of manufacturing the Cr photomask, a transparent substrate of, for example, quartz or glass with a chromium metal layer formed thereon using spattering and then is coated with an etching resist layer (photosensitive layer) over the chromium metal layer. After having exposed the etching resist layer to a given mask pattern with a HeCd laser of a wavelength of 442 nm and then developed the etching resist layer with, for example, an alkali solution, the chromium metal layer is etched so as thereby to reproduce the given mask pattern therein.
The inventor of this application has proposed in Japanese Patent Application No. 2000-163272, now open to the public as Japanese Unexamined Patent Publication No. 2001-343734, a photomask having a photosensitive layer sensitive to near-ultraviolet radiations or visible light. This photomask is easy of defect correction, better balanced in sensitivity and resolution, inexpensive in production, and less load on the environment in addition to having no necessity of having a metal layer. The photosensitive layer has the property of absorption that, while the photosensitive layer is, on one hand, low in absorbency in near-ultraviolet and visible regions before exposure and development in the process of manufacturing the photomask and the photosensitive layer after exposure and development absorbs light in the ultraviolet region adequately when the potomask is used.
Since exposing and developing the photosensitive layer is the unavoidable step in any process of manufacturing the photomask, in order for the photomask to be high in resolution and quality, the photosensitive layer has the necessity of having high sensitivity, mechanical strength and hardness, and satisfactory solvent resistance.
There have been know a variety of photosensitive materials. An example of such a photosensitive material is a colored pigment dispersed-radiation sensitive composition that is used for manufacturing color filters for liquid crystal display devices and solid-state image sensing devices, as disclosed in, for example, Japanese Unexamined Patent Publication No. 10-20496. This colored pigment dispersed-radiation sensitive composition, that is characterized in that a binding resin comprises a copolymers of an allyl acrylate monomer or an allyl methacrylate monomer and a monomer having an acid a group, has high sensitivity and large developing latitude and is excellent in adhesion. However, the colored pigment dispersed-radiation sensitive composition is intended for manufacturing color filters and is not applicable to manufacturing photomasks. In addition, since the colored pigment dispersed-radiation sensitive composition is not sensitive to light in the near-ultraviolet and visible regions, it is impossible to employ the pigment dispersed-radiation sensitive composition as the photosensitive layer of the photomask material indispensably sensitive to laser light in the near-ultraviolet and visible regions that have high radiation energy.
An example of an etching resist used for black matrices is a composition disclosed in, for example, Japanese Unexamined Patent Publication No. 10-39502 that consists of a binder resin, a compound having a specific chemical structure of ethylenically double bond, a photopolymerization initiator and a pigment. Since the binder resin is incapable of polymerizing and, in consequence, a layer of the etching resist is low in mechanical strength, there is the problem that exposed regions of the etching resist layer possibly swells as it is developed. This is conductive to a deterioration in the resolution of matrix. In addition, since the composition absorbs light in the near-ultraviolet and visible regions, it is impossible to employ the composition for an etching resists for a photosensitive layer indispensably sensitive to laser light in the near-ultraviolet and visible regions.
An example of a photo resist material used for colored filters is a composition disclosed in, for example, Japanese Unexamined Patent Publication No. 10-55064 that consists of a binder resin with a molecular weight distribution Mw/Mn of from 2.0 to 5.0, a compound with a specific chemical structure of ethylenically double bond, a photopolymerization initiator and a pigment. This composition has the same problems as the etching resist exemplified above.
An example of a colored photosensitive material used for color filters is a composition disclosed in, for example, Japanese Unexamined Patent Publication No. 7-98409 that employs a resin having an ethylenically double bond and a fluorine ring as a pigment dispersed resin. A photosensitive layer made of the colored photosensitive composition has high sensitivity to light for exposure even though it has no oxygen blocking layer operative to block off oxygen counteract photopolymerization. This colored photosensitive composition is not only unsuited for photosensitive transfer materials because the colored photosensitive composition has strong adhesion and is, in consequence, hard to be turned into a film, but also excludes laser light in the visible region from the use of exposure because the colored photosensitive composition is not sufficiently sensitive to laser light in the visible region.